This application is based on and claims priority from Japanese application No. HEI P03-261482 and Japanese application No. P04-96802, the disclosures of which are incorporated by reference herein.
The present invention relates to a zoom lens system which is highly susceptible to temperature and humidity variations. More particularly, the present invention relates to a telephoto-type, two-group or three-group zoom lens system for use with a compact camera, which has a shorter back focus than the zoom lens system for a single-lens reflex camera.
Heretofore, numerous telephoto-type two- or three-group zoom lens systems having a zoom ratio of about 2 or 3 have been known for use with compact cameras. Conventional zoom lens systems have an overall lens length (distance from the first surface to the image plane) at the narrow-angle or telephoto end which is greater than the focal length at the telephoto end.
However, if a zoom lens system whose overall length is greater than its focal length is assembled in a camera, the overall size of the equipment is not sufficiently compact. Thus, a smaller-sized zoom lens system is desired.
Accordingly, each of the lens groups used must be set to have a large power. However, if the power of each lens group is increased, a substantial amount of defocussing (e.g., focus shift) will occur if the lens barrel is even minutely deformed due to temperature or humidity changes. Compact cameras are typically equipped with a range finding optical system separate from the imaging lens system, and the focus adjusting position of the imaging lens system is prefixed with respect to the distance to the object. Therefore, if defocussing as described above results, it cannot be corrected and unfocused pictures are obtained.